path: root/fs
diff options
authorGu Zheng <guz.fnst@cn.fujitsu.com>2013-10-25 18:15:06 +0800
committerAl Viro <viro@zeniv.linux.org.uk>2013-10-25 10:46:40 -0400
commit05e16745c0c471bba313961b605b6da3b21a853d (patch)
tree72d6432126a32d984dd8189942818df6d1a391ff /fs
parentc7314d74fcb089b127ef5753b5263ac8473f33bc (diff)
seq_file: always update file->f_pos in seq_lseek()
This issue was first pointed out by Jiaxing Wang several months ago, but no further comments: https://lkml.org/lkml/2013/6/29/41 As we know pread() does not change f_pos, so after pread(), file->f_pos and m->read_pos become different. And seq_lseek() does not update file->f_pos if offset equals to m->read_pos, so after pread() and seq_lseek()(lseek to m->read_pos), then a subsequent read may read from a wrong position, the following program produces the problem: char str1[32] = { 0 }; char str2[32] = { 0 }; int poffset = 10; int count = 20; /*open any seq file*/ int fd = open("/proc/modules", O_RDONLY); pread(fd, str1, count, poffset); printf("pread:%s\n", str1); /*seek to where m->read_pos is*/ lseek(fd, poffset+count, SEEK_SET); /*supposed to read from poffset+count, but this read from position 0*/ read(fd, str2, count); printf("read:%s\n", str2); out put: pread: ck_netbios_ns 12665 read: nf_conntrack_netbios /proc/modules: nf_conntrack_netbios_ns 12665 0 - Live 0xffffffffa038b000 nf_conntrack_broadcast 12589 1 nf_conntrack_netbios_ns, Live 0xffffffffa0386000 So we always update file->f_pos to offset in seq_lseek() to fix this issue. Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 3135c2525c7..a290157265e 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -328,6 +328,8 @@ loff_t seq_lseek(struct file *file, loff_t offset, int whence)
m->read_pos = offset;
retval = file->f_pos = offset;
+ } else {
+ file->f_pos = offset;
file->f_version = m->version;